Spectacle lenses are most often provided with an identifying mark from which the manufacturer can be identified. This is especially important in the case of a claim or an objection which is sometimes made after the product has been used for a while. Accordingly, this type of identifying mark on the spectacle lens itself must be in a permanent form. On the other hand, the marking should not disturb the person wearing the spectacles during normal use thereof. More specifically, the marking should not be visible to such a person.
With non-rotational symmetrical spectacle lenses such as toric and bifocal lenses, the spectacle lens has a marking which provides the optician with a control so that he may fit the lens into the spectacle frame without difficulty. A marking of this type should likewise be invisible to a person wearing the spectacles.
It is known to apply a marking to a spectacle lens by means of a very fine mechanical engraving. This method is very expensive and requires substantial effort. It is further known to produce an etched marking by etching away a portion of the glass. However, this method requires that the entire remaining portion of the lens be covered with an enamel coating or the like which must later be removed. Accordingly, this method too requires a substantial expenditure. Markings are also known which are applied to the lens with a stamp in the form of the desired marking. In this method, certain substances are applied to the lens surface which cause the region of the marking to have a degree of wettability different from that of the remaining surface of the lens. This type of marking is made visible for a short time by exhaling onto the lens. The disadvantage of this kind of mark is that it lasts for only a limited time.
All of the methods described above have in common that they must be performed with a great deal of care and therefore with relatively large amount of effort so that on the one hand, a good visibility is achieved for the optician while, on the other hand, the person wearing the glasses will hardly notice the marking. This and other rather contradictory requirements can only be achieved by maintaining tight tolerances.
The tight tolerances of this kind are best controlled and maintained by means of a likewise known method by which a suitable substance is vaporized onto the spectacle lens with aid of a mask or template. The masks or templates have openings formed therein which correspond to the desired marking so that the substance is applied to the lens only in the form of the marking. With templates which are mounted directly in front of the spectacle lens even with only very limited spacing, there is however the disadvantage that the marking will not be sharply defined at the edges thereof.
Austrian Pat. No. 346,627 discloses masks made of a metal suspension and applied by vaporization. These masks are used in the production of dielectric coatings in patterned distribution, for example, for plates with phase rings, filter coatings which cover only a portion of the filter plate as well as for decorative lettering and ornamental patterns. The metal coating is utilized as a coating defining a mask which must be removed by dissolving the same using a dissolving solution after the dielectric coating is vaporized onto the plate.
Notwithstanding the good results obtained for a mass-produced article such as spectacle lenses with this type of method, it is evident that a method of this kind is also very expensive in terms of cost and effort because of the production of the masks, the vaporization procedure and the subsequent difficult removal of the masks.